Finally, many of the reported single-photon emitters \({\sim 2}\)  eV possess linearly polarized excitation and emission [1]}, [2]}, [3]}, [4]}, [5]}, [6]}, [7]}, [8]}, [9]}, [10]}, [11]}, indicating the anisotropic structural symmetry of the corresponding defects [12]}, [13]}, i.e. possibly belonging to
\(C_{2v}\) , \(C_2\)  or \(C_s\)  groups.
